Vehicle rearview mirror system

ABSTRACT

A vehicle rearview mirror system includes an electro-optic reflective element, an ambient light sensor that is operable to sense ambient light, a glare light sensor that is operable to sense glare light and a circuit that is responsive to the ambient glare light sensors which establishes a reflectance level of the reflective element. The circuit produces an output that is a function of light sensed by glare and ambient light sensors. The circuit compares an output of a charge accumulation device with a reference, and the circuit selectively connects the glare sensor and the ambient light sensor with the charge accumulation device. The mirror system may include a display operable to project light through the reflective element and may control the intensity of the display as a function of the glare light and ambient light.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/029,172, filed Feb. 11, 2008, now U.S. Pat. No. 7,453,057,which is a continuation of U.S. patent application Ser. No. 11/735,777,filed Apr. 16, 2007, now U.S. Pat. No. 7,329,850, which is acontinuation of U.S. patent application Ser. No. 10/955,694, filed Sep.30, 2004, now U.S. Pat. No. 7,205,524, which is a division of U.S.patent application Ser. No. 10/427,026, filed Apr. 30, 2003, now U.S.Pat. No. 6,918,674, which claims priority of U.S. provisionalapplications, Ser. No. 60/377,561, filed May 3, 2002; and Ser. No.60/426,227, filed Nov. 14, 2002, which are all hereby incorporatedherein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to vehicle rearview mirrorsystems and, more particularly, to such mirror systems havingself-dimming mirrors, and to such mirror systems having a display in arearview mirror.

BACKGROUND OF THE INVENTION

Automatic rearview mirrors which automatically control the glare fromthe headlights of following vehicles, or when driving away from thesetting sun, have been produced and installed in vehicles for manyyears. Glare reflected in these mirrors has been adjusted by employingmotorized prismatic mirrors, liquid crystal shutters and, mostsuccessfully, electrochromic mirror reflective elements in which thereflectivity of the mirror is responsive to an applied voltage. While avariety of light measuring and control systems have been proposed andused, such as described in U.S. Pat. No. 3,601,614 issued to Platzer,Jr. and U.S. Pat. No. 3,600,951 issued to Jordan et al., among others, aparticularly successful commercial system has relied on two cadmiumsulfide light sensors, one sensing ambient light levels and the othersensing rearward glare sources. Typical control systems utilizing thistype of devices are described in commonly assigned U.S. Pat. No.5,715,093 issued to Schierbeek et al.

Many of the characteristics of cadmium sulfide light sensors are wellsuited to the functional objectives of an automatic mirror controlcircuit, and their use has contributed to the cost effectiveness of themirror system in which they are used and the consequent commercialsuccess of these systems.

In recent years, efforts have been made to eliminate cadmium fromvehicle systems. In one such effort undertaken in Europe, the vehicle isdesigned to be recycled, and material, such as cadmium, is restricted.Consequently, it is desirable to utilize light sensors in automaticrearview mirror control circuits which are based upon alternativematerials and ideally which achieve the response in performance and costpreviously achieved with circuits utilizing cadmium sulfide devices. Inthis manner, the manufacturer can continue to offer the comfort andadvantages of glare control mirrors to the driving public at affordableprices.

Attempts have been made in the art involving vehicle rearview mirrorsystems having tandem light sensors and light signals that areintegrated over predetermined integration periods. Examples of such artinclude U.S. Pat. Nos. 6,008,486; 6,359,274; 6,379,013 and 6,402,328,the disclosures of which are hereby incorporated herein by reference.

It is also known to provide a display through a mirrored electrochromiccell of an electrochromic mirror, while blocking the view of the displaystructure or device through the mirrored surface. When such a display isimplemented in an interior rearview mirror assembly of a vehicle, it ispossible to provide the driver of the vehicle with the full use of themirror surface when the data display is not required or activated. Thisalso allows the use of a larger display area, and consequently, a largercharacter size, than is typically possible when the display is locatedin the mirror frame or bezel, or if a permanent non-mirrored displaywindow is provided within the mirror area. Such a display is commonlyreferred to as “display on demand”.

Although a display on demand provides the above benefits to a driver ofthe vehicle, such a display requires brightness or intensity control ofthe display for optimum readability in all lighting conditions.Traditional rearview mirror displays have a relatively constantbrightness background field on which characters are displayed, such as adark lens surface with low reflectivity or the like. In such displays,it is typical to control the display brightness according only toambient lighting conditions, such that in bright ambient lightingconditions, the display is bright enough to read, but in low ambientlighting conditions, the display is not so bright that it is annoying ordistracting to the driver of the vehicle. For example, a very brightdisplay in dark driving conditions can reduce the driver's ability todiscern detail in the forward view, since such a display may cause thedriver's pupils to adjust in order to accommodate the bright lightsource. However, because the reflectivity of a reflective element of anelectrochromic mirror is variable or adjustable, the intensity of thedisplay may be further controlled or adjusted to maintain a desiredcontrast ratio between the display and the reflected scene.

SUMMARY OF THE INVENTION

The present invention provides for the utilization of commerciallyavailable, low cost, silicon-based light-sensing devices in automaticrearview mirror control systems. The present invention also provides acontrol for a display through a mirrored surface of a vehicular rearviewmirror which is operable to adjust the intensity or brightness of thedisplay in response to the brightness of a scene rearward of thevehicle.

A vehicle rearview mirror system, according to an aspect of theinvention, includes an electro-optic reflective element, an ambientlight sensor that is operable to sense ambient light, a glare lightsensor that is operable to sense glare-producing light, and a circuitthat is responsive to the ambient and glare light sensors and whichestablishes a reflectance level of the reflective element. The circuitincludes a sensor-responsive device and a controller. Thesensor-responsive device produces an output that is a function of lightsensed by one of the glare and ambient light sensors. The controllerconnects one of the glare and ambient light sensors at a time with thesensor-responsive device in order to establish the ambient and glarelight levels and thereby the reflectance level of the reflectiveelement.

A vehicle rearview mirror system, according to another aspect of theinvention, includes an electro-optic reflective element and ambientlight sensor that is operable to sense ambient light, a glare lightsensor that is operable to sense glare-producing light, and a circuitthat is responsive to the ambient and glare light sensors and whichproduces an output that establishes a reflectance level of thereflective element. The circuit includes a charge accumulation device, acomparison function and a controller. The comparison function comparesan output of the charge accumulation device with a reference. Thecontroller connects one of the glare and ambient light sensors at a timewith the charge accumulation device and establishes the ambient andglare light levels and thereby the reflectance level of the reflectiveelement from the comparison function. The controller establishes lightlevels as a function of time for the output of the accumulation deviceto reach the reference.

A vehicle rearview mirror system, according to another aspect of theinvention, includes an interior rearview mirror assembly having aninterior electro-optic reflective element and at least one exteriorrearview mirror assembly having an exterior electro-optic reflectiveelement. The system further includes an ambient light sensor that isoperable to sense ambient light, a glare light sensor that is operableto sense glare-producing light, and a circuit that is responsive to theambient and glare light sensors and which establishes reflectance levelsof the interior reflective element and the exterior reflective element.The circuit includes a sensor-responsive device and a controller. Thesensor-responsive device produces at least one output that is a functionof light sensed by the glare and ambient light sensors. The controllerconnects one of the glare and ambient light sensors at a time with thesensor-responsive device to establish the ambient and glare light levelsand thereby the reflectance levels of the interior reflective elementand the exterior reflective element.

The various aspects of the present invention utilize common integrationelements to measure the light sensors sequentially such that errors dueto, for example, component variations are corresponding for both glareand ambient measurements. This facilitates use of mass-produced siliconsensors and avoids the need for matching of components. The variousaspects of the invention also achieve sensing of wide input light leveldynamic range using off-the-shelf light sensors.

According to another aspect of the present invention, an electrochromicrearview mirror system includes a display which is viewable through amirrored surface of the rearview mirror system. The mirror systemincludes a display intensity control which is operable to adjust anintensity of the display in at least part of its operating range inresponse to a brightness level of a scene rearward of the vehicle.

The control may be operable as a function of the ambient light levels(from a forward facing and/or rearward facing light sensor) and a valuerepresentative of the amount of light impinging the rearward facingrearview mirror surface. The control may be further responsive to amodulating effect of an electrochromic cell of the electrochromicrearview mirror system.

According to another aspect of the present invention, an electrochromicrearview mirror system includes a rearview mirror assembly having anelectrochromic reflective element and a display operable to projectlight through the reflective element. The mirror system includes acontrol operable to adjust an intensity of the display. The mirrorsystem also includes an ambient light sensor operable to detect ambientlight levels generally at the mirror assembly and to generate an outputsignal indicative of an ambient light value, and a glare sensor operableto detect glare or light impinging on the reflective element of themirror assembly and to generate an output signal indicative of a glarelight value. The control is operable to control the intensity of thedisplay as a function of a modulation effect of the electrochromicreflective element and the glare value and ambient light value.

The control may control the display intensity of the display in responseto a function of the ambient light value and time to limit rapidfluctuations of the display intensity. The control may control a fullycompensated display intensity via the following function or equation:I(fc)=Fn(ME*GV/AV)*Fn(AV,t)*ME−½; where ME is the modulation effect ofthe reflective element, GV is the glare value, AV is the ambient lightvalue and t is time.

Therefore, the present invention provides an electrochromic rearviewmirror system incorporating a display and a display intensity controlwhich includes an intensity adjustment responsive in at least part ofits operating range to the brightness of the rearward scene. The displayintensity is adjusted to maintain an appropriate intensity level whereit is easily viewable by the driver of the vehicle. The displayintensity is bright enough to be seen clearly yet not so bright to annoyor distract the driver. The display intensity is also controlled toprovide a sufficient contrast ratio against the variable backgroundbrightness of the reflected scene.

These and other objects, advantages, purposes and features of thepresent invention will become apparent upon review of the followingspecification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electrical schematic diagram of a vehicle rearview mirrorsystem in accordance with the present invention;

FIGS. 2 a and 2 b are diagrams illustrating the operation of therearview mirror system in FIG. 1;

FIG. 3 is the same view as FIG. 1 of an alternative embodiment thereof;

FIG. 4 is the same view as FIG. 1 of another alternative embodimentthereof;

FIG. 5 is the same view as FIG. 1 of yet another alternative embodimentthereof;

FIG. 6 is a top plan view of a vehicle equipped with a rearview mirrorsystem in accordance with the present invention;

FIG. 7 is a block diagram of the vehicle rearview mirror system of FIG.6;

FIG. 8 is a diagram illustrating the operation of the rearview mirrorsystem in FIG. 1; and

FIG. 9 is a block diagram of another vehicle rearview mirror system inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now specifically to the drawings, and the illustrativeembodiments depicted therein, a vehicle rearview mirror system 10includes an electro-optic reflective element 12, an ambient light sensorA that is operable to sense ambient light, a glare light sensor G thatis operable to sense glare-producing light, and a circuit 14 thatresponds to ambient light sensor A and glare light sensor G and whichestablishes a reflectance level of reflective element 12 (FIG. 1).Circuit 14 includes a controller 16, which may be defined by amicrocontroller, such as a microcomputer, which produces an output 18indicative of a desired reflectance level of reflective element 12, anda driver 20 which produces an output signal at 22 which establishes thereflectance level of reflective element 12. Driver 20 may be of variousconfigurations. One such configuration includes a switching device whichis operable by controller 16 at a particular duty cycle to establish thereflectance level of reflective element 12, such as disclosed incommonly assigned U.S. Pat. No. 6,056,410, issued to Hoekstra et al.,and U.S. Pat. No. 6,089,721, issued to Schierbeek, the disclosures ofwhich are hereby incorporated herein by reference.

Circuit 14 includes a sensor-responsive device 24 defined by a capacitorC and a comparator 26 that is connected with ambient light sensor A andglare light sensor G. Comparator 26 may be a separate device or may beincorporated as one or more inputs of microcomputer 16. Circuit 14includes switches S1, S2 and S3, which are electronic switches, such asfield effect transistors (FET), that are operated by outputs ofcontroller 16. Alternatively, bipolar transistors may be used. Switch S1selectively connects glare light sensor G between a voltage source V anda terminal 28 of capacitor C. The other terminal of capacitor C isconnected to chassis or ground. Switch S2 selectively connects ambientlight sensor A with terminal 28 of capacitor C. Switch S3 is in parallelwith capacitor C. Terminal 28 is connected with the non-inverting inputof comparator 26. The inverting input of comparator 26 is connected witha reference voltage. The reference voltage may be developed by any knownmeans, such as by a voltage divider connected with voltage source V, orthe like. In the embodiment illustrated in FIG. 1, the reference voltageis fixed. However, in the other embodiments described below, thereference voltage may be variable. Also, other component arrangementsmay perform the same function. By way of example, the capacitor may beconnected with the voltage source and the light sensors may be connectedbetween the capacitor and ground.

Controller or microcomputer 16 operates switches S1, S2 and S3 toselectably charge and discharge capacitor C. For example, controller 16may first actuate switch S1. Referring to FIGS. 2 a and 2 b, with switchS1 actuated, capacitor C is charged by a current through glare lightsensor G developed by voltage V. The current charging capacitor C is afunction of the amount of light sensed by glare light sensor G. The morelight sensed by glare light sensor G, the faster capacitor C is charged.As capacitor C is charged, a voltage developed at terminal 28 iscompared by comparator 26 against the reference voltage. When thevoltage across capacitor C reaches the reference voltage, controller 16causes switch S1 to open. The accumulation time interval between theclosing of switch S1 and the opening of switch S1 is defined as theglare time interval Tg. After a short duration of time after switch S1has been opened, controller 16 causes switch S3 to close for a period oftime, thereby discharging capacitor C. After another brief duration oftime, controller 16 closes switch S2 which causes a current to flowthrough ambient light sensor A, thereby charging capacitor C at a ratethat is a function of the light sensed by ambient light sensor A. Whenthe voltage at terminal 28 reaches the reference voltage of comparator26, the output of comparator 26 changes state which is monitored bycontroller 16. In response, controller 16 causes switch S2 to open,thereby defining the end of ambient charge accumulation period Ta. Aftera brief duration of time, controller 16 again closes switch S3, therebyagain discharging capacitor C.

FIG. 2 a illustrates a situation in which glare light sensor G issensing a relatively low glare light level, and ambient light sensor Ais sensing a relatively low ambient light level. This results inrelatively long accumulation periods Tg and Ta. FIG. 2 b illustrates asituation where glare sensor G senses a relatively high glare lightlevel, and ambient light sensor A senses a relatively high ambient lightlevel. Therefore, in the situation illustrated in FIG. 2 b, accumulationperiods Tg and Ta are relatively short. Controller 16 responds to thelength of accumulation periods Tg and Ta in order to determine a ratioof glare light level to ambient light level, or G/A. By determining theratio G/A and by utilizing common capacitor C and comparator 26, causesof common mode error are significantly reduced. This is because anyerrors will be common to both determinations Tg and Ta. Therefore, whena ratio is taken, the common sources of errors are cancelled as would beunderstood by the skilled artisan. The initiation of a cycle ofdetermination of Tg and Ta may be initiated at the end of the priordetermination of Tg and Ta. This would provide a free running system.Alternatively, each cycle could be initiated at a fixed time that is setin order to accommodate a maximum allowable value. This may simplify thesoftware run by microcomputer 16. However, both techniques are equallyeffective at determining G/A.

As disclosed in commonly assigned U.S. Pat. No. 4,793,690 issued toGahan et al., the disclosure of which is hereby incorporated herein byreference, it is known that the glare tolerance G_(T) may be calculatedby the following equation:

G _(T) =CM ^(N) +B;  (1)

where C and B are constants, M is a measure of modified ambient lightlevel, and N is a constant. Modified ambient light level utilizestime-adapted filtering to remove transients from the sensed ambientlight and to match the adaptation of the eye as taught in the '690patent, reference above. N may be varied, such as between 0.8 and 1.3,to adjust the shape of the resulting curve.

For values of N that are close to unity, the ratio of G_(T)/A isreasonably linear as illustrated between points A1 and A2 in FIG. 8. Thecircuit 14 determines a value of G/A, which is also a ratio, asillustrated by a generally horizontal line in FIG. 8. Conveniently,controller 16 may make a straightforward comparison of the value of G/Aas measured by circuit 14 and compare it with the value of GT/A andgenerate an appropriate drive signal with driver 20 in order to adjustthe reflectance level of reflective element 12 to bring the value ofglare sensed by the driver in line with the glare tolerance of thedriver. This ratio of G/A causes variables that may affect the sensingof glare and ambient light to be common and, therefore, cancelled. Oneexception may be dark current generated by the sensors, which varies bythe duration of the exposure time. Therefore, other supplementaltechniques are provided herein to further reduce dark current errors.

In the illustrated embodiment, glare light sensor G and ambient lightsensor A may be semiconductor devices, namely, phototransistors,photodiodes, or the like. Such semiconductor devices are relativelyinexpensive and readily available and do not create difficulties withend-of-product-life disposal. The present invention is capable ofproducing a value of G/A that is relatively linear within the range of0.01 lux to 100 lux.

In an embodiment illustrated in FIG. 3, a vehicle rearview mirror system110 includes a circuit 114 with a second capacitor C2 and a fourthswitch S4. Switch S4 is under the control of controller 16 and isoperable to selectively place capacitor C2 in parallel with capacitorC1. Under generally low ambient light conditions, controller 16 wouldcause switch S4 to be opened, thereby using only capacitor C1 to becharged by the respective glare light sensor G and ambient light sensorA. In relatively high light conditions, controller 16 could cause switchS4 to be conducting thereby placing capacitor C2 in parallel with C1.This allows the voltage at terminal 128 to accumulate to the level ofthe reference voltage in a longer accumulation period than capacitor C1alone. Thus, controller 16 may utilize capacitor C1 alone and determinewhether the level of voltage on terminal 128 reaches the referencewithin the maximum duration set for the accumulation period. It shouldbe understood that, although one additional switched capacitor isillustrated in FIG. 3, a series of switched capacitors may beindividually controlled by controller or microcomputer 16 in a similarfashion, as would be understood by the skilled artisan. This techniquemakes better use of the resolution of the microcomputer's internaltimer.

A vehicle rearview mirror system 210 is illustrated in FIG. 4 in which avoltage reference 227 provided to comparator 26 is produced bymicrocomputer 16. Controller or microcomputer 16 may produce reference227 at a level which is a function of light levels sensed by the circuit224. Thus, for example, in high light conditions, controller 16 may setreference 227 at a relatively high level because the voltage at terminal228 will rise relatively quickly in the manner set forth in FIG. 2 a. Incontrast, during low light conditions, controller 16 may produce a lowerreference voltage 227. In this fashion, the voltage at terminal 228 willreach the reference 227 at a shorter accumulation period than wouldotherwise occur. This allows the accumulation period to be within ashorter range of periods and thereby accommodate a greater range oflight levels by the vehicle rearview mirror system.

Although the vehicle rearview mirror system, according to the variousembodiments disclosed herein, reduces sources of common mode errors, itmay be desirable to provide additional functions to further reducedark-current errors. For example, at low light levels and relativelyhigh temperatures, dark currents can greatly exceed the current producedas a result of sensed light. It may be desirable to provide compensationfor temperature variations. In an embodiment illustrated in FIG. 5, avehicle rearview mirror system 310 includes a circuit 314 having atemperature compensation in the form of shielded light sensor D which isnot exposed to light. In the same fashion that controller 16 accumulatescharge with one of the glare sensors G and ambient sensors A connectedwith capacitor C, circuit 314 also selectively connects sensor D withcapacitor C during a third accumulation period. This is accomplished bycontroller or microcomputer 16 actuating a fifth switch S5 to placesensor D in series between voltage source V and capacitor C. Because thedark current produced by sensor D will be similar to the dark currentproduced by sensor G and sensor A, controller 16 can compensate for darkcurrent by utilizing the information obtained from measuring the darkcurrent produced by sensor D.

Circuit 314 may also include temperature compensation in the form of atemperature sensor 40 monitored by microcomputer 16 in order to measureambient temperature conditions. Based upon a lookup table or a formulastored in controller or microcomputer 16, controller 16 may utilize thetemperature reading detected by temperature sensor 40 in order todetermine a value of dark current produced by sensors G and A. This alsoprovides an additional technique for further reducing the effect of darkcurrents especially during extreme temperature conditions. It should beunderstood that the temperature compensation techniques disclosed hereincan be used separately or in combination.

As indicated above, automatic dimming circuitry used in electrochromicmirror assemblies (such as disclosed in U.S. Pat. Nos. 4,793,690;4,886,960; 4,799,768; 4,443,057 and 4,917,477, the entire disclosures ofwhich are hereby incorporated by reference herein) may utilize one ormore (typically two) photo sensors (such as photo resistors or photodiodes or photo transistors) to detect glaring and/or ambient lighting.For example, a silicon photo sensor, such as a TSL235RLight-to-Frequency converter (available from Texas AdvancedOptoelectronic Solutions Inc. of Plano, Tex.) can be used as such photosensors. Such light-to-frequency converters comprise the combination ofa silicon photodiode and a current-to-frequency converter on a singlemonolithic CMOS integrated circuit. Alternately, a photo sensor thatconverts ambient light to a digital signal capable of direct feed into amicroprocessor (or into a vehicle bus system, such as a LIN or CANsystem or an SMBus) can be used. For example, a TSL2550 light sensor canbe used that converts light intensity to a digital output (and isavailable from Texas Advanced Optoelectronic Solutions Inc. of Plano,Tex.). The TSL2550 Light-to-Digital photo sensor uses an all-silicontechnique that combines two photodetectors to measure light brightnessas perceived by the human eye, and calculates light intensity in unitsof lux. One photo sensor is sensitive to both visible and infraredlight, while the other is sensitive only to infrared light. By such acombination, the infrared component of detected light is compensatedfor, and the output of the part is approximate the response of the humaneye, thus obviating a need for a photopic filter. The ratio of infraredto visible light can be calculated and used to determine the type oflight source (for example, incandescent or sunlight). Thus, for example,glaring light from headlamps (typically incandescent or high intensitydischarge) can be distinguished from moonlight, sunlight, neon light,and the like.

Vehicle rearview mirror system 10 is illustrated in FIG. 6 in use with avehicle 42. Vehicle 42 is shown having an interior rearview mirrorassembly 44 and exterior rearview mirror assembly 46 a on a driver sideof the vehicle and exterior rearview mirror assembly 46 b on a passengerside of the vehicle. Circuit 14 may produce reflectance levels for aninterior reflective element 112 in interior rearview mirror assembly 44and the exterior reflective elements 212 a in exterior mirror assembly46 a and 212 b in exterior mirror assembly 46 b. Circuit 14 may bepositioned in interior rearview mirror assembly 14 with the reflectiveelements produced therein communicated via vehicle communication bus 48.Alternatively, circuit 14 may be positioned in more than one of themirror assemblies 44, 46 a, 46 b and may individually control therespective reflectance level for that mirror reflective element. Ifcircuit 14 is positioned within interior rearview mirror assembly 44,ambient light sensor A may face in a generally forward direction withrespect to the vehicle and glare sensor G facing generally rearward withrespect to the direction of the vehicle. Alternatively, circuit 14 maybe positioned in an exterior rearview mirror assembly 46 a, 46 b withglare light sensor G and ambient light sensor A facing generallyrearward with respect to the vehicle. In such circumstances, the glarelight sensor may be aimed along a generally horizontal axis and theambient light sensor along another axis that deviates from thehorizontal axis. The deviation may be between 10 degrees and 70 degrees,as disclosed in commonly assigned U.S. Pat. No. 5,659,423 issued toSchierbeek et al., the disclosure of which is hereby incorporated hereinby reference.

Circuits 114, 214, 314 may be manufactured using application specificintegrated circuit (ASIC) technology. In the case of a circuit positionwithin interior rearview mirror assembly 44, an ASIC could be utilizedcombining one of the light sensors G and A with all or a portion of therest of circuits 14, 214 and 314 with the other light sensor G, A byitself or with the portion of the circuit not included with the otherlight sensor. If both light sensors are on the same side of the circuit,such as disclosed in Schierbeek et al. '423, referenced above, a singleASIC could be utilized.

Thus, the present invention provides automatic dimming circuitry withoutthe use of tandem light sensors and without light signals that areintegrated over predetermined integration periods.

Referring now to FIG. 9, an electrochromic rearview mirror system 50 fora vehicle may include a mirrored element and a display 52 which isviewable through the mirrored element. The rearview mirror system 50 mayinclude an interior rearview mirror assembly 54 and/or one or moreexterior, side mounted rearview mirror assemblies 56. The electrochromicmirror assembly or assemblies 54, 56 may utilize the principlesdisclosed in commonly assigned U.S. Pat. Nos. 5,140,455; 5,151,816;6,178,034; 6,154,306; 6,002,544; 5,567,360; 5,525,264; 5,610,756;5,406,414; 5,253,109; 5,076,673; 5,073,012; 5,117,346; 5,724,187;5,668,663; 5,910,854; 5,142,407 or 4,712,879, which are herebyincorporated herein by reference, or as disclosed in the followingpublications: N. R. Lynam, “Electrochromic Automotive Day/NightMirrors”, SAE Technical Paper Series 870636 (1987); N. R. Lynam, “SmartWindows for Automobiles”, SAE Technical Paper Series 900419 (1990); N.R. Lynam and A. Agrawal, “Automotive Applications of ChromogenicMaterials”, Large Area Chromogenics: Materials and Devices forTransmittance Control, C. M. Lampert and C. G. Granquist, EDS., OpticalEngineering Press, Washington (1990), which are hereby incorporated byreference herein, and in U.S. patent application Ser. No. 09/792,002,filed Feb. 26, 2001 by Schofield et al. for VIDEO MIRROR SYSTEMSINCORPORATING AN ACCESSORY MODULE, now U.S. Pat. No. 6,690,268, which ishereby incorporated herein by reference.

The display 52 may comprise a display-on-demand type of display, such asthe types disclosed in commonly assigned U.S. Pat. Nos. 5,668,663 and5,724,187, and/or in U.S. patent application Ser. No. 10/054,633, filedJan. 22, 2002 by Lynam et al. for VEHICULAR LIGHTING SYSTEM, now U.S.Pat. No. 7,195,381; and Ser. No. 09/792,002, filed Feb. 26, 2001 bySchofield et al. for VIDEO MIRROR SYSTEMS INCORPORATING AN ACCESSORYMODULE, now U.S. Pat. No. 6,690,268, which are all hereby incorporatedherein by reference. With such a display, it is not only desirable toadjust the display brightness according to ambient lighting conditions,but it is also desirable to adjust the display brightness such that asufficient contrast ratio is maintained against the variable backgroundbrightness of the reflected scene. Also, it may be desirable tocompensate for changes in transmission of the electrochromic deviceeffected to control rearward glare sources, in order that the displaybrightness appears to be maintained at a generally constant level.

The present invention may include an interior rearview mirror assemblywhich is mounted to an interior surface of the windshield or at theheadliner of the vehicle. The interior rearview mirror assembly mayinclude a transflective one way mirror, such as disclosed in commonlyassigned U.S. patent application Ser. No. 10/054,633, filed Jan. 22,2002 by Lynam et al. for VEHICULAR LIGHTING SYSTEM, now U.S. Pat. No.7,195,381, which is hereby incorporated herein by reference. The mirrorreflective element (behind which the display element or screen isdisposed so that the image displayed is visible by viewing through themirror reflective element) of the interior mirror assembly may comprisea transflective mirror reflector such that the mirror reflective elementis significantly transmitting to visible light incident from its rear(i.e. the portion furthest from the driver in the vehicle), with atleast about 15% transmission preferred, at least about 20% transmissionmore preferred, and at least about 25% transmission most preferred,while the mirror reflective element is simultaneously substantiallyreflective to visible light incident from its front (i.e. the positionclosest to the driver when the interior mirror assembly is mounted inthe vehicle), with at least about 60% reflectance preferred, at leastabout 70% reflectance more preferred, and at least about 75% reflectancemost preferred.

A transflective electrochromic reflective mirror element may be used(such as is disclosed in U.S. patent application Ser. No. 09/793,002,entitled VIDEO MIRROR SYSTEMS INCORPORATING AN ACCESSORY MODULE, filedFeb. 26, 2001, now U.S. Pat. No. 6,690,268 and in U.S. Pat. Nos.5,668,663 and 5,724,187, the entire disclosures of which are herebyincorporated by reference herein) that comprises an electrochromicmedium sandwiched between two substrates. The front substrate (i.e.closest to the driver when the interior mirror assembly is mounted inthe vehicle) may comprise a glass substrate having a transparentelectronic conductive coating (such as indium tin oxide or doped tinoxide) on its inner surface (and contacting the electrochromic medium).Optionally, the front substrate of the twin-substrate electrochromiccell that sandwiches the electrochromic medium comprises a glasssubstrate having a thickness of about 1.6 millimeters or less;preferably, about 1.1 millimeters or less. The rear substrate (i.e.furthest from the driver when the interior mirror assembly is mounted inthe vehicle) may comprise a glass substrate having a transflectivemirror reflector on the surface thereof that the electrochromic mediumcontacts (such a configuration being referred to as a “third-surface”reflector in the electrochromic mirror art).

For example, the mirror reflector may comprise a transparentsemiconductor/metal conductor/transparent semiconductor multilayerstack, such an indium tin oxide/silver/indium tin oxide stack. Forexample, a third-surface electrochromic mirror reflective element may beused comprising a front substrate comprising an about 1.1 mm thick glasssubstrate having a half-wave indium tin oxide (ITO) coating of about 12ohms/square sheet resistance on its inner surface; a rear substratecomprising an about 1.6 mm thick glass substrate having a transflectivemirror reflector thereon comprising an about 350 angstrom thick silvermetal layer sandwiched between an about 800 angstrom thick indium tinoxide transparent semiconductor layer and another about 800 angstromthick indium tin oxide transparent semiconductor layer; and with anelectrochromic solid polymer matrix medium, such as is disclosed in U.S.Pat. No. 6,245,262 (the entire disclosure of which is herebyincorporated by reference herein), disposed between the transflectivemirror reflector of the rear substrate and the half-wave indium tinoxide layer of the front substrate. Visible light reflectivity of thetransflective electrochromic mirror element may be about 60-65%; andlight transmission may be about 20-25%. For example, with a TFT LCDvideo display disposed behind the rear substrate of such a third-surfacetransflective electrochromic mirror reflective element in a“display-on-demand” configuration, the presence of (and image displayedby) the video display screen is only principally visible to the driver(who views through the transflective mirror reflective element) when thevideo display element is powered so as to project light from the rear ofthe mirror reflective element.

Optionally, in applications in which a TET LCD video screen isimplemented, a single high-intensity power LED, such as a white lightemitting LED comprising a Luxeon™ Star Power LXHL-MW1A white lightemitting LED having (at a 25 degree Celsius junction temperature) aminimum forward voltage of 2.55 volts, a typical forward voltage of 3.42volts, a maximum forward voltage of 3.99 volts, a dynamic resistance of1 ohm and a forward current of 350 milliamps, and available fromLumileds Lighting LLC of San Jose, Calif., may be used as a backlightfor the TFT LCD video screen. Alternately, a plurality of such singlehigh-intensity power LEDs (such as an array of two or of four such powerLEDs) may be placed behind the TFM LCD video screen so that the intensewhite light projected from the individual single high-intensity powerLEDs passes through the TFT LCD element and through the transflectiveelectrochromic element, and may produce a display intensity as viewed bythe driver of at least about 200 candelas/sq. meter; more preferably atleast about 300 candelas/sq. meter; and most preferably at least about400 candelas/sq. meter. Alternately, cold cathode vacuum fluorescentsources/tubes may be used for backlighting and optionally can be used inconjunction with LED backlighting.

The electrochromic rearview mirror system of the present inventionincludes two image sensors or illumination sensors: one forward facingsensor 58 which may provide a basis for calculating or determining avalue representative of ambient lighting conditions around the vehicle,and one rearward facing sensor 60 which may be useful in determining thedegree of glare impinging the mirror surface and consequently beingreflected toward the driver's eyes. The sensor or sensors 58, 60 may beimaging sensors, and may be imaging array sensors, such as a CMOS sensoror a CCD sensor or the like, such as disclosed in commonly assigned U.S.Pat. Nos. 5,550,677; 5,670,935; 5,796,094; and 6,097,023, which arehereby incorporated herein by reference. Optionally, the control 62 ofthe present invention may be operable to receive data (which isindicative of ambient light levels) from one or more existing imagingsensors on the vehicle, such as an imaging sensor for a vehicle visionsystem, such as a vehicle vision system utilizing the principlesdisclosed in U.S. Pat. Nos. 5,550,677; 5,670,935; and 6,201,642, and/orin U.S. patent application Ser. No. 09/199,907, filed Nov. 25, 1998 byBos et al. for WIDE ANGLE IMAGE CAPTURE SYSTEM FOR VEHICLE, now U.S.Pat. No. 6,717,610, and Ser. No. 09/372,915, filed Aug. 12, 1999 by Boset al. for VEHICLE IMAGING SYSTEM WITH STEREO IMAGING, now U.S. Pat. No.6,396,397, which are hereby incorporated herein by reference, an imagingsensor for a lane departure warning system, an imaging or light sensorfor a rain sensor, such as disclosed in U.S. Pat. Nos. 6,313,454;6,353,392; and 6,320,176, and/or the like, without affecting the scopeof the present invention.

A value representative of ambient lighting conditions may otherwise bederived from a combination of forward and rearward facing light sensors.The resultant value representative of the ambient light level is used toestimate the sensitivity of the driver's eyes and thus provide theappropriate degree of intensity reduction of the reflected image toavoid reduced forward vision capability.

The electrochromic rearview mirror system of the present invention, asequipped or associated with a forward facing light sensor 58 and arearward facing light sensor 60, may calculate an ambient light value AVbased on the value of the forward facing light sensor or a combinationof values from the forward and rearward facing light sensors. Theambient light value AV is representative of the ambient light levelsurrounding the vehicle.

The ambient light value AV is then used to determine a driver's eyes'sensitivity value SV, based on a relationship between the ambient lightvalue AV and the sensitivity value SV, as described in commonly assignedU.S. Pat. Nos. 4,793,690 and 4,799,768, which are hereby incorporatedherein by reference. The value of the sensitivity SV may be divided intotwo values: SV1, which represents the value above which a light sourceis considered a discomfort at a particular ambient lighting level, andSV2, which represents the value above which a light source becomesdebilitating at a particular ambient lighting level. A debilitatingcondition arises when the ability to discern detail in the general fieldof view is reduced. A relationship is selected where the sensitivityvalue SV, as a function of the ambient light value AV, is between thesensitivity values SV1 and SV2.

A light value GV, which is representative of the quantity of lightimpinging the rearward facing sensor, and thus the rearview mirrorsurface, is determined from the value of the rearward facing lightsensor. In those cases where the sensed light value GV exceeds themaximum acceptable sensitivity value SV, a modulating effect ME of theelectrochromic cell in the light path is used to reduce the light valueGV toward the sensitivity value SV, such that GV*ME=SV, to the extentthat a sufficient modulating effect is available. The degree ofmodulation ME may be controlled by the voltage V applied to theelectrochromic element, so that the degree of modulation ME is afunction of the applied voltage V.

When a display is associated with the rearview mirror, the intensity ofthe display is typically controlled between a maximum intensity value I1and a minimum intensity value I2 as a function of the ambient lightcondition. The display intensity I is thus a function of the ambientlight value AV and time t, and may be a step function, a linearfunction, a logarithmic function, or any other continuous function,without affecting the scope of the present invention. The time t isincluded in the relationship to avoid any potentially annoying rapidfluctuations of the display intensity. When the display is viewedthrough a non-reflecting window or region of the electrochromic cell, itis desirable to correct for the varying modulation of the cell. Themodulation effect ME is based on a double pass through theelectrochromic medium, while the light from the display only passes oncethrough the electrochromic medium. Therefore, the display intensity maybe corrected to a corrected intensity value I_((c)), according to thefollowing relationship:

I _((c)) =I*ME ^(−½).  (2)

When a display-on-demand information display system is used, brightrearward scenes reduce the contrast ratio between the active regions ofthe display and the reflected background scene. In order to correct thissituation and render the display readable, it is desirable to increasethe display illumination by a function of the ratio of the brightness ofthe rearward scene (after modulation, if such modulation is present) tothe ambient light value which controls the nominal illuminationintensity. In other words, the display illumination or intensity I maybe controlled according to the following relationship:

$\begin{matrix}{I = {{{Fn}\left( \frac{\left( {M\; E*G\; V} \right)}{A\; V} \right)}.}} & (3)\end{matrix}$

The function of equation (3) may have a value of one (1) for all caseswhere the value of (ME*GV)/AV is less than one, since the relationshipor function of the intensity I (which is a function of the ambient lightlevel or value AV and time t, as discussed above) may establish anappropriate display intensity regardless of the darkness of thebackground field in such situations. Therefore, the relationshipcontrolling the fully compensated display intensity I_((fc)) becomes thefollowing:

$\begin{matrix}{I_{({fc})} = {{{Fn}\left( \frac{\left( {M\; E*G\; V} \right)}{A\; V} \right)}*{{Fn}\left( {{A\; V},t} \right)}*M\; {E^{\frac{- 1}{2}}.}}} & (4)\end{matrix}$

Therefore, the present invention provides an electrochromic rearviewmirror system which incorporates a display and a display intensitycontrol, which further includes an intensity adjustment responsive in atleast part of its operating range to the brightness of the rearwardscene. The display intensity control is operable as a function of theambient light levels (from a forward facing light sensor and/or arearward facing light sensor) and a value representative of the amountof light impinging the rearward facing rearview mirror surface. Thedisplay intensity control is further responsive to a modulating effectof the electrochromic cell.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the principles of the presentinvention which is intended to be limited only by the scope of theappended claims, as interpreted according to the principles of patentlaw including the doctrine of equivalents.

1. A rearview mirror system for a vehicle, said rearview mirror systemcomprising: an electro-optic reflective element; an ambient light sensorthat is operable to sense ambient light; a glare light sensor that isoperable to sense glare-producing light; and a circuit responsive tosaid ambient and glare light sensors, wherein said circuit compares anoutput of a charge accumulation device with a reference, said circuitselectively connecting said glare sensor and said ambient light sensorwith said charge accumulation device; and wherein said circuit isoperable to establish a reflectance level of said reflective element,said circuit producing an output that is a function of light sensed bysaid glare and ambient light sensors.